1. Field of the Invention
The present invention relates to a structure of a shutter device, and, more particularly, to a mechanism for preventing a shutter blade from bounding.
2. Description of the Related Art
In a related focal-plane shutter device, a shock-absorbing member for restricting bounding of a shutter blade is provided near a movement completion position of the shutter blade. When the shutter blade collides with the shock-absorbing member in a plane that is perpendicular to a movement direction of the shutter blade when the movement of the shutter blade is completed, shock generated by suddenly stopping the shutter blade is absorbed by the shock absorbing member, so that the bounding of the shutter blade occurring when the shutter blade is stopped can be restricted. Rubber is frequently used for the shock-absorbing member.
When the collision between the shutter blade and the rubber is repeated, scraping of the rubber is eventually started by the collision of the shutter blade, thereby producing wear powder. Unlike a film camera whose film can be replaced, in a digital camera, an image pickup element is accommodated in the camera body at all times. Therefore, when the wear powder adheres to the image pickup element, the wear powder may appear in an image.
To restrict the production of wear powder, Japanese Patent Laid-Open No. 09-005831 proposes a structure in which a surface of a shock-absorbing member that comes into contact with a shutter blade is covered with a material that is harder than the shock-absorbing member.
According to this structure, since the hardness of the surface of the shock-absorbing member that comes into contact with the shutter blade is made high due to the coating layer, wear powder is not produced often. In addition, shock that is produced when the shutter blade and the coating layer collide with each other can be absorbed by the rubber existing below the coating layer.
However, even if a shock-absorbing member whose rubber surface is provided with a coating layer using a material that is harder than rubber is used, the production of wear powder cannot be prevented from occurring. This is caused by the difference between the amount of deformation of the coating layer and the amount of deformation of the rubber when the shutter blade and the shock-absorbing member collide with each other.
The amount of deformation of the coating layer is less than the amount of deformation of the rubber when the shutter blade and the shock-absorbing blade collide with each other. This difference between the deformation amounts causes a force that tries to separate the coating layer and the rubber from each other to act upon the surface where the coating layer and the rubber are joined. Therefore, when the number of collisions between the shutter blade and the shock-absorbing member increases, the coating layer and the rubber are eventually peeled off from each other, thereby causing a flake of the peeled coating layer to adhere to the image pickup element.